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Cholesteric liquid crystal light modulators

Inactive Publication Date: 2010-10-12
KENT STATE UNIV
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Benefits of technology

[0010]This present embodiments provide a method of fabricating liquid crystal light modulating devices comprising a cholesteric liquid crystal. In general, the present invention provides a method for fabricating light modulating devices, comprising a pair of substrates with transparent conductive electrodes, providing alignment layers for planar alignment, and depositing a cholesteric liquid crystal between the substrates. The cholesteric liquid crystal forms a planar texture with an alignment layer providing strong surface anchoring for liquid crystal molecules. And more particularly, it provides a cholesteric liquid crystal light modulating device whose spectral wavelength is electrically tunable. The cholesteric liquid crystal may include a heterogeneous species to enhance its reflectivity.
[0012]At least one or more of the foregoing aspects, together with the advantages thereof over the known art relating to liquid crystal displays, are accomplished by the invention as herein after described and claimed. The phase-separated polymer or polymer network in cholesteric liquid crystal may be induced by polymerization, solvent evaporation or heat. Furthermore, this invention provides a method of fabricating full color reflective cholesteric displays using single panel. The device can also be built on substrates that are flexible and with a patterned wall structure to provide physical support to the substrates against external stress and mechanical shock. These patterned wall structures include but not limited to substrates with grooved structure, patterned polymer walls, polymer cups and polymer dispersed liquid crystal structures where high polymer content will enhance the structural stability.

Problems solved by technology

While the feasibility has been demonstrated, there is a loss in reflective brightness.
The bottleneck for the full color cholesteric displays to be realized commercially resides in the production yield and cost.
For example, to display a full color image it requires three color cholesteric films and electronic drivers which increase the cost of the display.
Furthermore, the shift register of pixels from separate panels causes parallax problem.
As a result, the yield in producing full color displays is low because of complexity in manufacturing process.
Without strong surface anchoring, there are insufficient cholesteric pitches to reflect incoming light in the normal direction.
Consequently, these methods yield low reflectivity and short spectrum tuning range.
As a consequence, high switching voltage and slow response time are major challenges associated with the in-plane switched color technique.
The negative aspects include broadening of reflective bandwidth and low reflectivity.

Method used

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[0032]As shown in FIG. 4, a field-induced blue shift in cholesteric liquid crystal is illustrated wherein the reflected wavelength is a function of applied voltage (a) and the reflectivity is a function of switched spectral wavelength (b). The reflective wavelength of the cholesteric liquid crystal is 695 nm with 45% reflectivity at zero voltage. As the voltage exceeds 15V, the pitches in the bulk are deformed by the voltage because of weak anchoring and thus, the pitches in the middle layers are extended. Consequently, the liquid crystal molecules in the bulk start to compress the pitches near the boundary layers so the pitches near the boundary layers are shortened. The spectral wavelength is switched to reflect a red at 16V with 25% reflectivity, green at 25V with 15% reflectivity and blue color at 40V with 12.5% reflectivity. Because the oriented liquid crystal molecules are no longer in a planar structure, the number of layers contributing to the reflectance decreases. Therefor...

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Abstract

This invention relates to a method of fabrication of liquid crystal light modulating devises having electrically tunable spectral wavelength and more particularly, to a cholesteric liquid crystal display with electrically switchable colors. The cholesteric light modulators may be fabricated by applying a plurality of layers to maximize the light modulation. It also features a polymer composite or polymer-network stabilized cholesteric liquid crystal with electrically switchable Bragg reflected wavelength within a predetermined range of spectral wavelength.

Description

[0001]The present application claims priority from and the benefit of the filing date of Provisional Patent Application Nos. 60 / 836,093 and 60 / 836,094, both filed Aug. 7, 2006.BACKGROUND[0002]A cholesteric liquid crystal will adopt a helical structure with the director rotating around an axis perpendicular to the substrate surfaces in an electro-optical cell with homogeneous alignment. Because of the self-assembled helical structure of cholesteric liquid crystal, in the planar texture where cholesteric helix is aligned vertically, the incident light is decomposed into its right and left circular components with one component reflected and the other transmitted. The unique ability of a cholesteric liquid crystal to reflect light comes from their helical superstructure. The central reflected wavelength (λo) in a direction normal to the surface can be described as λ0= n·p= n·(C·HTP)−1, where p is the helical pitch, in which the director rotates 360 degree, n is the average refractive i...

Claims

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Application Information

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IPC IPC(8): G02F1/13
CPCG02F1/13718G02F2001/13478G02F2001/13775G02F1/13478G02F1/13775
Inventor CHIEN, LIANG-CHYLU, SHIN-YING
Owner KENT STATE UNIV
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